glGetPolygonStipple returns to mask a $32 ~times~
32$ polygon stipple pattern. The pattern is packed into memory as if glReadPixels
with both height and width of 32, type of GL_BITMAP, and format of GL_COLOR_INDEX
were called, and the stipple pattern were stored in an internal $32 ~times~
32$ color index buffer. Unlike glReadPixels, however, pixel transfer operations
(shift, offset, pixel map) are not applied to the returned stipple image.